자료유형  

 학위논문

Control Number  

0017160192

International Standard Book Number  

9798382717036

Dewey Decimal Classification Number  

540

Main Entry-Personal Name  

Murphey, Corban Graef Edward.

Publication, Distribution, etc. (Imprint  

[S.l.] : The University of North Carolina at Chapel Hill., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

126 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.

General Note  

Advisor: Cahoon, James F.

Dissertation Note  

Thesis (Ph.D.)--The University of North Carolina at Chapel Hill, 2024.

Summary, Etc.  

요약Confining light into a small space is a key aim in many areas of photonics research. If you try to do this with traditional optics, you quickly run into a fundamental limit: the Abbe diffraction limit. This dictates that a beam of light with wavelength λ can only be confined to a size of approximately λ/2. When working with visible or even ultraviolet light, this means it is very challenging to focus that beam into a space less than ~100 nm in size, and with modern technological components getting smaller and smaller each year, other means are necessary to confine light into small spaces. Two phenomena in particular have emerged as strategies for squeezing light down to the nanoscale: plasmon resonances and optical bound states in the continuum (BICs).Plasmon resonances, which are the result of collective oscillations of surface electrons at a metal-dielectric interface, are able to confine incident light to a deep-subwavelength, or less than λ/10, scale. However, since plasmonic nanomaterials often consist solely of metals, the rapid electron motion in the particle can result in large Ohmic losses, which results in sometimes undesirable heating effects, large spectral linewidths, and short surface plasmon polariton propagation lengths. In comparison, dielectric materials like Si have much lower losses and can sustain narrow linewidths and long propagation distances, but because of their low free carrier concentration, they are not generally able to confine light on the same sub-wavelength scale as metallic plasmonic materials. If these two classes of materials were combined into a single nanostructure, such that the electric field generated by the plasmon resonance were confined into a dielectric core, it would be possible to achieve simultaneous sub-wavelength confinement and low loss. We were able to synthesize such a structure-an epitaxial Si nanowire (NW) core coated with a shell of Au- via a combination of vapor-liquid-solid (VLS) NW growth and metal sputtering. Examining these hybrid NWs using both optical simulations and experimental extinction measurements, we found that they support Mie resonances with quality factors (Q-factors) enhanced up to ~30 times compared to pure dielectric structures and plasmon resonances with optical confinement enhanced up to ~5 times compared to pure metallic structures. We also show that the spectral response of the Mie and plasmon resonances can be reproduced with temporal coupled mode theory (TCMT) and the Fano lineshapes can be attributed to the combination of the high Q-factor resonances, Mie-plasmon coupling, and phase delay of the background optical field. Our work demonstrates a bottom-up method for synthesizing free-standing, cylindrically symmetric, core-shell nanowires that efficiently trap light on a deep sub-wavelength scale, which has implications for many applications in photonics and optoelectronics.As alluded to above, Si NWs have attracted significant attention recently due to their photonic properties, such as their ability to support axially guided optical modes. By periodically modulating dopant gas flow during VLS growth and then wet-chemical etching the as-grown NWs, we can create semi-infinite geometric superlattices, or GSLs. Under specific geometric parameters, Si NW GSLs can support BICs of different orders, which have theoretically infinite lifetimes and Q-factors, and are perfectly isolated from surrounding radiation. If one purposefully detunes those idealized geometric parameters, a quasi-BIC (qBIC) is formed. qBICs retain the high Q-factor and lifetimes of true BICs, but are able to couple with external radiation and manifest as absorption and scattering features. This allows for the identification of trends in different qBICs and their behavior with respect to other Si NW resonances, such as Mie resonances or other qBICs and BICs. We simulated and synthesized a suite of NW GSL geometries that support several qBICs in the visible through NIR spectral regions. Through analysis of the simulated electric and magnetic field profiles, we have also developed a labeling scheme to identify and track different modes across different parameters. We then experimentally detected these qBICs with two, home-built, single-nanowire spectroscopy apparatuses: one measuring extinction and the other measuring photothermal absorption. Our work demonstrates the ability to precisely control the presence, position, and properties of qBICs in Si NW GSLs, with the potential to enhance the ability of photovoltaic Si NWs to harvest the solar spectrum.

Subject Added Entry-Topical Term  

Chemistry.

Subject Added Entry-Topical Term  

Nanoscience.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Physical chemistry.

Subject Added Entry-Topical Term  

Analytical chemistry.

Index Term-Uncontrolled  

Chemical vapor deposition

Index Term-Uncontrolled  

Nanophotonics

Index Term-Uncontrolled  

Nanowires

Index Term-Uncontrolled  

Plasmonics

Index Term-Uncontrolled  

Spectroscopy

Added Entry-Corporate Name  

The University of North Carolina at Chapel Hill Chemistry

Host Item Entry  

Dissertations Abstracts International. 85-11B.

Electronic Location and Access  

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Control Number  

joongbu:655352